Electronic pressure sensing device

ABSTRACT

An electronic pressure sensing device comprises a pressure sensing/transmitter module including at least one pressure sensor having a pair of opposed sensing elements, and a pair of inlet ports on the module to supply fluid under pressure to the sensing elements, and a plurality of adaptors each having a pair of outlet ports for connection to the inlet ports on the module whereby each adaptor can be selectively coupled to the module, each adaptor being capable of being connected to a different configuration of pressurized fluid supply to feed the associated supply to at least one of the inlet ports on the module, the module further including electronic means for interpreting and transmitting the values of pressure sensed by the sensing elements.

[0001] This invention relates to an electronic pressure sensing device, and more particularly to such a device for use with fluid filters to determine pressure loss across the filter.

[0002] Determining the pressure loss across a filter is an every day occurrence and is a very important factor in determining the filter element(s) potential life expectancy and also the costs associated with power consumption.

[0003] Mechanical differential pressure gauges and pop-up indicators are offered by most leading filter manufacturers and these generally bolt directly on top of the filter.

[0004] A further enhancement of these mechanical devices is to attach a magnet to the moving parts and, at a pre-set differential pressure, have it coincide with an electrical reed switch thus opening up many options for an electrical interface.

[0005] A still further enhancement includes a light fitted within the differential gauge casing such that it can send out a visual (flashing) warning when it reaches a pre-set differential pressure.

[0006] Even more elaborate designs include differential pressure gauges with built in electronic sensing which can output linear signals (as opposed to a single switch point) which link directly to hand held computers for determining the cost of electrical power consumption against the cost of fitting new filter elements.

[0007] The manufacturing market is moving more and more towards computerisation, where every aspect of a production line can be controlled via an electronic interface. There are several standard data transfer interfaces such as 4-20 mA (current loop), RS-232 & 485 (serial type) as well as various field bus systems such as Profibus-FMS, Inter-Bus S. & Ethernet. Each of these systems has it's own advantages and disadvantages and some operate in a more refined, higher level than others, therefore representing the vast diversity of actual applications. The most common interface used with gauge and differential pressure transmitters is the 4 to 20 ma (current loop) signal.

[0008] Unfortunately, the cost of fitting proprietary electronic differential pressure sensors/transmitters is generally very high, not only due to the cost of the sensor/transmitter itself but also due to the cost of associated pipes, fittings, valves, brackets etc. plus the cost of manpower.

[0009] This invention addresses the problems concerned with fitting such devices.

[0010] According to the present invention there is provided an electronic pressure sensing device comprising a pressure sensing/transmitter module including at least one pressure sensor having a pair of opposed sensing elements, and a pair of inlet ports on the module to supply fluid under pressure to the sensing elements, the device further comprising a plurality of adaptors each having a pair of outlet ports for connection to the inlet ports on the module whereby each adaptor can be selectively coupled to the module, each adaptor being capable of being connected to a different configuration of pressurised fluid supply to feed the associated supply to at least one of the inlet ports on the module, the module further including electronic means for interpreting and transmitting the values of pressures sensed by the sensing elements.

[0011] The sensing/transmitter modules may consist of a metal or plastic enclosure containing at least one piezoresistive sensor integrated with and sealed in a fluid tight manner to two sensor manifolds, one to each end of said sensor, which incorporate male connections with captive double O-ring seals which extend from the front of the module and with which pressure tight connection to any of the adapters may be made.

[0012] Furthermore, each sensor manifold may be ported (drilled) in various ways to allow the sensing/transmitter module to operate in at least three different measurement formats by allowing the pressure, directed by the adapters from the application, to be directed to the appropriate sensor pressure port.

[0013] Said module may contain all the necessary circuitry with which to accept a 12-24 VDC electric power input and to output a current or voltage signal directly proportional to the pressure being measured with an accuracy greater than ½% of the pressure range being measured.

[0014] An integrated electrical connector provides means with which to make input and output electrical connections while maintaining an IP65 seal. A yellow LED may extend from the rear of the case to give a positive indication of power supply to the device.

[0015] By way of example only, the invention will now be described in greater detail with reference to the accompanying drawings of which:

[0016]FIG. 1 gives an isometric representation of the assembled device;

[0017]FIG. 2 is a multi-view detail of the rear sensing/transmitter module;

[0018]FIG. 3 is a multi-view detail of a piezoresistive pressure sensor;

[0019]FIG. 4 is a multi-view detail of a sensor manifold;

[0020]FIG. 5 is a multi-view detail of printed circuit board (electronic circuitry);

[0021]FIG. 6 indicates the way in which the printed circuit board assembly is retained by the enclosure;

[0022]FIG. 7 is a multi-view detail of the enclosure trim lid detail;

[0023]FIG. 8 is a multi-view detail of a front adapter incorporating a 2 hole design;

[0024]FIG. 9 is a multi-view detail of a front adapter incorporating a 4 hole design;

[0025]FIG. 10 is a multi-view detail of a front adapter incorporating threaded pipe pressure connections;

[0026]FIG. 11 gives a graph representing the transmitter's electrical outputs in relation to sensed pressure;

[0027]FIG. 12 represents a concept whereby the rear sensing/transmitter module is fastened to the front adapters by means of built-in plastic snap mechanisms;

[0028]FIG. 13 represents the various ways in which the sensor manifolds can be ported (drilled) in order to allow the rear/sensing transmitter module to be used in various pressure measurement format.

[0029] Sensor Manifold Porting Options

[0030] Please refer to FIG. 13.

[0031] The sensor manifolds 2, 3 may be ported in at least four different ways to allow the manifolds to be used in three different finished sensing/transmitter module product configurations, 1, 6, 15.

[0032] In the differential pressure sensing configuration 1, both manifolds 2, 3 are drilled from the front port 73, 74, through to the first sensor cavity therefore exposing one end 4 of the sensor 29 to the higher of two pressures and the second end 5 of the sensor 29 to the lower of two pressures.

[0033] In the gauge pressure sensing configuration 6, one manifold 7 is drilled from the front port through to the first sensor cavity 13 therefore exposing one end 8 of the sensor 36 to pressure. The second manifold 14 is drilled from the outside of the case 9 through to the first sensor cavity 10 so that the second end 12 of the sensor 36 is exposed to atmospheric pressure. Since the pressure port 11 of the second manifold is not drilled through to the first sensor cavity 10, the sensor's low pressure port 11 is isolated from pressure and therefore allows the device to read gauge pressure.

[0034] In the differential and gauge pressure sensing configuration 15, the first manifold 16 is drilled from the front port 17 through to both sensor cavities 18, 19 so that one end 20, 21 of both sensors 32, 33 is exposed to the higher of two pressures. The second manifold 22 is drilled from the front port 23 through to the first sensor cavity 24 so that the second end 25 of the first sensor 32 is exposed to the lower of two pressures. A third hole is drilled from the outside of the case 26 into the second sensor cavity 27 such that the second end 28 of the second sensor 33 is exposed to atmospheric pressure. This allows the first sensor 32 to read differential pressure and the second sensor 33 to read gauge pressure.

[0035] One Design Facilitates Up to Six Different Measurement Formats

[0036] Please refer to FIG. 13.

[0037] The device utilises up to two pressure sensors and one temperature sensor thereby allowing up to six different measurement formats each with its own current or voltage output.

[0038] Format 1: Differential Pressure 1.

[0039] Utilises one pressure sensor 29 in the first sensor manifold position to measure the difference in pressure between the higher 30 and lower 31 of two pressures.

[0040] Format 2: Differential & Gauge Pressure 15.

[0041] Utilises two pressure sensors 32, 33, to simultaneously measure the differential pressure between the higher 34 and lower 35 of two pressures and the gauge pressure of the higher 34 of the two pressures.

[0042] Format 3: Differential Pressure & Temperature.

[0043] Utilises one pressure sensor in the first sensor manifold position to measure the difference in pressure between the upstream and downstream pressures. Additionally a temperature sensor allows measurement of the ambient temperature at the application.

[0044] Format 4: Gauge Pressure 6.

[0045] Utilises one pressure sensor 36 in the first sensor manifold position to measure the gauge pressure.

[0046] Format 5: Gauge Pressure & Temperature.

[0047] Utilises one pressure sensor in the first sensor manifold position to measure the upstream gauge pressure. Additionally a temperature sensor allows measurement of the ambient temperature at the application.

[0048] Format 6: Differential, Gauge & Temperature.

[0049] Utilises two pressure sensors, to simultaneous measure the differential and upstream gauge pressures. Additionally a temperature sensor allows measurement of the ambient temperature at the application.

[0050] Reversible Rear Sensing/Transmitter Module

[0051] Please refer to FIG. 2.

[0052] Since the rear sensing unit 37 has specific high 38 and low 39 ports, it has been designed so that it can be flipped over thus allowing the high or low pressure ports to be easily directed to their proper sources as dictated by the selected front adapter.

[0053] Detachable Front Adapters

[0054] Unless otherwise noted, please refer to FIGS. 8, 9 and 10.

[0055] Said device has been designed as a two piece system with the first piece being a front adapter and the second the actual sensing/transmitter module. All front adapters have a common connection 40, 41, 42 for mating to the rear sensing/transmitter module. Each adapter offers a different connection format to allow the sensing/transmitter module to be connected directly to many different applications. The adapters are fastened to the rear sensing/transmitter module via two self tapping screws 43, 44, 45. A fluid tight seal is made between the adapters and the rear sensing/transmitter module via two sets of double O-ring seals held captive on the male pressure ports 38, 39 (FIG. 2) of the sensor manifolds which extend out the front of the sensing/transmitter module.

[0056] Two Hole Front Adapter:

[0057] Utilises a design whereby two special bolts 46, with a flat ground on one side 47 are used to both hold the device in position and also allow the pressure to pass either through or around the bolts and through said conduits 49 to the sensor. O-ring seals 50 are made between the screw head and the top of the adapter as well as between the adapter and the application 51 in order to properly direct the pressure from the application 55 to the sensing/transmitter module.

[0058] Four Hole Front Adapter:

[0059] Utilises a design whereby two bolts 52 are used to hold the device in position whilst two separate ports 53 are used to direct pressure to the pressure manifolds. O-ring seals 54 are made between the inner set of holes 53 and the application 56.

[0060] Pipe Connection Adapter:

[0061] Utilises a design whereby two pipe port connections 57,58 are connected to the two pressure ports 59,60 such that pipe/tube fittings can be used for non-direct mount applications.

[0062] Sensor Manifolds Facilitate Simplified Assembly

[0063] Unless otherwise noted, please refer to FIG. 5.

[0064] The device utilises two sensor manifolds/conduits 61,62, which are designed to fit over either end of the sensor's pressure ports 63, 64 (FIG. 3) and seal to the sensor in a fluid tight manner via an O-ring seal 65. Pins, located on the top and bottom edges of the manifolds 66 (FIG. 4), key into holes provided in the printed circuit board. Once engaged into the holes 67 (FIG. 6), the manifolds are mechanically fixed in position parallel to each other with the sensor(s) trapped between. The sensor is soldered to the card 68 (FIG. 6) thus locking the assembly into place.

[0065] In order to maintain the spacing between the internal manifolds, and to ensure that the manifolds do not spread apart far enough to compromise the integrity of the O-ring seal, square extensions at the front of the manifolds 69 (FIG. 4) engage into notches moulded into the front of the enclosure 70 (FIG. 6). This connection is the only point of contact between the printed circuit board assembly and the enclosure therefore eliminating many possible component interference problems.

[0066] Although two sensor manifolds are employed in the design they maybe the same part. The manifolds have been designed in a symmetrical manner such that they can be flipped over for use in both positions.

[0067] Potting/Encapsulation

[0068] Once assembled, the rear sensing/transmitter module is filled with an electrically non (low) conductive potting material. The potting acts to hermetically seal the sensors so that the devices accuracy may be maximised. O-ring seals between the sensor manifolds and the sensors keep the potting from entering the sensor's pressure ports. Additionally, the potting acts to strengthen the assembly thereby allowing higher operating pressures to be achieved than would otherwise be possible.

[0069] Enclosure Cap Trim Piece

[0070] Unless otherwise noted, please refer to FIG. 7.

[0071] Once the sensor/printed circuit board assembly (FIG. 5) has been properly located within the enclosure and the unit has been filled with potting compound, a trim piece (FIG. 7) may be inserted into the front of the case. The trim piece includes two pins 71, which extend into the potting and lock the piece in place once the potting has set. Furthermore the trim piece acts to ensure that the sensor manifolds have been seated into their proper position before the potting sets.

[0072] Snap Fit Front Adapter Option

[0073] Unless otherwise noted, please refer to FIG. 12.

[0074] As an alternate fastening method to the self tapping screws for securing the front adapters to the rear sensing/transmitter module, clips 72 may be moulded onto the front adapters which engage into notches 73 in the rear sensing/transmitter module. This would eliminate the need for screws and would speed up assembly and disassembly of the two parts of the device in the field.

[0075] Pressure Range Selection

[0076] Please refer to FIG. 11.

[0077] The electronic sensing device may be factory calibrated to a virtually infinite number of pressure ranges 74. The current family of piezoresistive sensors has 7 different members ranging in pressure ranges from 0.34 to 17 bar. Any of these sensors may be used in this device. The device's sensing range does not have to line up exactly with the raw sensor's nominal ratings—ie. a device utilising a 0-1000 mbar sensor may be calibrated 0-500 mbar or 0-769 mbar.

[0078] Ample Size Conduit Ports

[0079] The cross sectional area of the holes and conduits are of great enough size so that they do not unduly restrict or create internal pressure losses which may be realised by momentary flow created in the conduit by fluctuations in pressure at the pressure source. Such fluctuation could affect the accuracy and/or response of the transmitter.

[0080] Double O-Ring Seal

[0081] Please refer to FIG. 2.

[0082] The ends of the sensor manifolds/conduits 38,39 have a double O-ring seal to ensure that no leakage occurs between the rear sensing/transmitter module and the front adapter.

[0083] Temperature Compensation

[0084] For applications where it is necessary to compensate the sensor's output due to excessive fluid temperature fluctuation, the standard sensor as utilised in the standard design may be replaced by a higher end sensor with built in temperature compensation. By using the higher end sensor, no further changes are required to the device.

[0085] Factory Calibration

[0086] Each rear sensing/transmitter module can be calibrated prior to assembly. Once calibrated, the unit is filled with potting compound thus eliminating the possibility of field calibration. This feature provides a lower product cost as a seal does not have to be made through the case for each tuning potentiometer. Additionally, the unit cannot be easily bumped out of adjustment.

[0087] Electrical Connection Options

[0088] Depending on the number of outputs required, the rear sensing/transmitter module may utilise different electrical connectors including but not limited to:

[0089] DIN 43650-C: Used for devices with up to 4 input/output connections. Connector has built in screw terminals which facilitates field connections. This connection type is the most common type used on said devices.

[0090] 12 mm Round Multi-pin Connector: Used for devices with up to 8 input/output connections.

[0091] Flying Leads: May be used with any device with any number of input/output connections. Consists of multi-conductor wire with suitable strain relief at point of entry into the sensing/transmitter module. Length of leads may be dictated by the application. 

What I claim and desire to secure by Letters Patent is:
 1. An electronic pressure sensing device comprising a pressure sensing/transmitter module including at least one pressure sensor having a pair of opposed sensing elements, and a pair of inlet ports on the module to supply fluid under pressure to the sensing elements, the device further comprising a plurality of adaptors each having a pair of outlet ports for connection to the inlet ports on the module whereby each adaptor can be selectively coupled to the module, each adaptor being capable of being connected to a different configuration of pressure fluid supply to feed the associated supply to at least one of the inlet ports on the module, the module further including electronic means for interpreting and transmitting the values of pressures sensed by the sensing elements.
 2. A device as claimed in claim 1 and including one pressure sensor the two sensing elements of which are arranged to detect a higher fluid pressure and a lower fluid pressure respectively thereby to determine a differential between said pressures.
 3. A device as claimed in claim 1 and including one pressure sensor a first sensing element of which is arranged to detect a fluid pressure and the second sensing element being subjected to atmospheric pressure whereby the device determines gauge pressure.
 4. A device as claimed in claim 1 and including two pressure sensors one sensing element of each sensor being arranged to detect a common higher fluid pressure, the other sensing element of a first of the sensors being arranged to detect a lower fluid pressure, and the other sensing element of the second sensor being subjected to atmospheric pressure, whereby the device determines the differential between the higher and lower pressures and the gauge pressure.
 5. A device as claimed in claim 1 in which the module comprises an outer housing, a first manifold within the housing including a first inlet port extending from the housing, and a second manifold within the housing including a second inlet port extending from the housing, the manifolds defining therein cavities in which are received the sensing elements of at least one sensor.
 6. A device as claimed in claim 1 in which the adaptors are coupled to the module by snap-fit connections therebetween.
 7. A device as claimed in claim 1 in which each adaptor includes means for attaching it to a source of fluid under test whereby higher pressure fluid flows to and through one outlet port and lower pressure fluid flows to and through the other outlet port. 